When resurfacing an asphalt road surface, at least a portion of the upper surface of the roadway is milled by specialized equipment so a new layer of asphalt can be deposited. The milling operation, which can also be referred to as cold planing, asphalt milling, or profiling, can be carried out at any desired depth depending on the resurfacing operation. Typically, a road surface is milled, and the material removed from the road is collected for recycling. Material suitable for recycling is ground and used as aggregate in new pavement. Milling operations in general are also used to control heights and clearances of other road structures such as curb reveals, manhole and catch basin heights, shoulder and guardrail heights, overhead clearances and the like in both finished and unfinished road surfaces.
Milling is generally performed by construction equipment called milling machines, such as cold planers and rotary mixers. These machines typically use a large rotating drum for removing and grinding the road surface. The drum is usually enclosed in a drum enclosure that shields the surroundings from flying debris and contains the milled material, which, in the case of at least a cold planer, is collected and deposited on a conveyor for loading onto a waiting truck. Many milling machines use an up-cut configuration, in which the drum rotates in the reverse direction to the drive wheel or tracks, which helps drive the milled material up and into a conveyor. This configuration also creates considerable amounts of dust and other airborne debris, which can be controlled by various methods including fluid spraying and using vacuum collectors. The fluid spray operates to cool the cutting drum and also help contain or settle dust. A typical milling machine will carry a reservoir onboard that feeds the fluid spray system. However, milling machines may operate in remote areas where fluid is not readily accessible and must be delivered by truck. Fluid replenishment also requires the machine to stop operation and thus increase the time required to complete a project.